Combined electromagnetic fuze and electric detonator



COMBINED ELECTROMAGNETIC FUZE AND ELECTRIC DETONATOR Filed Fab. 1'. 1950 w. J. Kl ROEGER ErAL July 23, 1957 G m mtu m 9/l/ R N v 5 WWW N m w n N T. e Es f G 15. f S F 2 FIG. 2. 7;

COMBINED ELECTROMAGNETIC FUZE AND ELECTRIC DETONATOR Film Feb. 1, 1.950

y 1957 w. J. KROEGER ETAL 2 Sheets-Sheet 2 IN VEN TORS GERALD E. HIRT. WILLIAM J. KROEGER. @LMf L/EW FEG. ll.

ORNEYS.

CUMBINED ELECTROMAGNETIC FUZE AND ELECTRIC DETONATOR William J. Kroeger and Gerald E. Hirt, Philadelphia,

Pa., assignors to the United States of America as represented by the Secretary of War Application February 1, 1950, Serial No. 141,802

7 Claims. (Cl. 102-702) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment of any royalty thereon.

Our invention relates broadly to combinations of electromagnetic fuzes and electric detonators for various types of projectiles, rockets, and the like. -More particularly, it relates to the incorporation of new and useful improvements in the design and operation of electromagnetic fuzes and parts associated with electric detonators, and to the addition of a safety inductance shunt .to the electromagnetic fuZe-electric detonator circuit so as to prevent accidental ignition of the explosive charge contained within a projectile.

Our invention resides in the unique manner by which electromagnetic fuzes are caused to become operative, and in the novel fashion by which the function of electric detonators are controlled. As will become evident later, our device will be seen to be superior toprior art devices in that it is much smaller, much safer, lighter in weight, more simplified in design, and more effective in operation.

The use to which our invention can be put is very extensive because it can be applied to any kind of projectile, such as that shot from guns, artillery pieces or the like; or it can be applied to any kind of rocket, such as that launched from a bazooka or other type of launcher often used aboard ship, on aircraft, tanks, and in other places. Additional uses are possible since many variation and modifications of our device may be made without departing from our inventive concept. For the purpose of the present disclosure only, this specification will concern the application of our invention to a conventional bazooka rocket.

Broadly stated, the object of our invention is to provide a small, light-weight, simply constructed electromagnetic fuze-electric detonator combination whose circuit has a very small time constant.

A more specific object is to provide an electromagnetic fuze-electric detonator combination which will be in-.

capable of operation when subjected to accidental physical shock or to stray electric or magnetic fields.

We obtain the foregoing and other objects and advantages of our invention by providing a slidably secured plunger, a coil, a permanent magnet, an electric detonator and a safety inductance shunt. When the projectile, rocket, or the like, so equipped with our invention is shot or launched into the air it reaches or exceeds a certain threshold velocity, i. e., the velocity at which the fuze will generate suflicient electrical energy to activate the detonator. Upon striking a target, the coil moves rapidly past the magnet, thereby generating a voltage surge. The electrical energy developed is transmitted to an electric detonator which is thereby activated and caused to ignite an explosive charge carried within the projectile.

If, before firing the projectile or rocket, the coil and the magnet should be accidentally moved relative to each other, it would be virtually impossible for the plunger to move the magnet at the proper speed to develop enough electrical energy to ignite the detonator. Ordinarily, too, if the projectile or rocket were subjected to stray electric or magnetic fields, the electrical energy developed likewise would not be sufficient to ignite the detonator. In both the above cases, our safety inductance shunt, acting as a low resistance, would cause the current to by-pass the detonator.

A clearer understanding of our invention will be obtained from an inspection of the following specification and the accompanying drawings wherein:

Fig. 1 is a plan view, partly in section, of a conventional bazooka rocket which is equipped with our invention;

Fig. 2 is a longitudinal section taken on line 22 of Fig. 1, much of the intermediate region having been removed for reasons of simplicity;

Fig. 3 is a completed transverse section taken along line 33 of Fig. 2 and looking in the direction from the rockets front or leading end to its rear or trailing end;

Fig. 4 is a portion of a completed longitudinal section taken along line 4-4 of Fig. 2;

Fig. 5 is a portion of a completed transverse section taken along line 55 of Fig. 2;

Fig. 6 is a transverse section taken along line 66 of Fig. 2;

Figs. 7, 8 and 9 are portions of completed transverse sections taken along lines 77, -8-8 and 99, respectively, of Fig. 2, some wires having been removed for convenience in drawing;

Fig. 10 is an enlarged view of a corresponding portion of the rockets nose shown in Fig. 2;

Fig. 11 and 11A are fragmentary longitudinal sections similar to corresponding nose portions of the Fig. 2 rocket, but showing subsequent stages of operation; and

Fig. 12 is a schematic representation of the electrical circuit involved in our invention.

As reference to Fig. 1 will show, the rocket to which our inventive device has illustratively been applied is a conventional bazooka projectile which consists primarily of a safety cap 16, a nose 17, a truncated ogive 18, a body 19, an adapter 20, a detonator housing 21, a hollow cylindrical motor 22 containing the propellant 23, and a tail assembly 24 having a plurality of fins 25.

Other components of the bazooka rocket, such as a cone which is confined between truncated ogive 18 and body 19, an explosive charge contained Within body 19 and launching means located in tail assembly 24, are not shown for reasons of simplicity because those skilled in the art undoubtedly are aware of their presence and their respective purposes.

Our inventive electromagnetic fuze is contained in the rockets nose 17; and the novel safety inductance shunt, together with other elements associated with the electric detonator, are contained in detonator housing 21. T herefore, only those members will be discussed in detail, the prior art having adequately described the remaining components of the conventional bazooka rocket.

THE ELECTROMAGNETIC FUZE The nose Figs. 1 and 2 show nose 17 to have a truncated conical portion 26 at its leading or forward end, and a cylindrical, externally threaded portion 27 at its trailing or rear end, the two forming at their juncture the shoulder 28. Conical portion 26 has the same taper as the leading end 29 of truncated ogive 18 and, when nose 17 is attached to the ogive by means of threaded portion 27, the lateral surface of conical portion 26 is substantially continuous with leading end 29. Following attachment of nose 17 to ogive 18, the ogive is staked at 30 into oppositely located wrench grooves 31 in the noses conical portion 26.

Located on nose 17, near the flat leading end of conical portion 26, is a right angled, circumferential groove 32 whose sides are parallel and perpendicular, respectively, to the axis of the nose (see Figs. 2, 11-1 lA). Those figures also show that nose 17 contains a series of axially located recesses progressively increasing in size from the leading end to the trailing end. Proceeding from the leading end of nose 17 those recesses are a plunger recess 33, a ball recess 34, a recess slidably containing the ball ring 35, a recess containing a two-piece coil shield 36 and shear plate 37, and an internally threaded recess containing the end plug 38. Between plunger recess 33 and ball recess 34 is the inclined shoulder 39 (see Figs. 2, 10, 11 and llA); and located in the wall of plunger recess 33 is a semi-cylindrical blind groove 40 (see Figs. 2, 11 and MA). More will be said about the nose parts later.

Ball ring, coil and coil shield Ball ring 35, slidably encircling a plunger, later to be described, and slidably accommodated in nose 17 (see Figs. 2, 11, 11A), comprises the following critical entities: a larger diametered recess 41 at its upper end, an inclined shoulder 42, and a smaller diametered recess 43. The lower or trailing end of ball ring 35 projects a short distance into the recess containing coil shield 36 (see Figs. 2, 11 and 11A).

The metallic coil shield 36 is composed of two pieces, a hollow ring-like body 45 and a complementary cover 46 which is pressed into the top open end thereof. For best operation of our inventive device, coil shield 36 should have sufiicient electrical resistance to help damp out eddy currents, and it should be so dimensioned that the magnetic reluctance of that part of the circuit is small. a grooved ring form 47 having suitable electrical insulating properties, is a coil 48 composed of approximately 70 turns of #28 enameled wire. The coil preferably should have low leakage losses, and it should present a reasonably low impedance to the circuit.

Insulator, magnet, shear plate and terminal post One end 49 of coil 48 passes outside the shield through an insulator i pressed into an opening in one side of coil form 47 and shield body 45 (see Fig. 2). The other end of coil 43 passes through a suitable opening in coil form 417 and is soldered or otherwise fastened to shield cover 46 as at the location A shown in Figs. 2 and 12.

Slidably fitting inside shield body 45 and shield cover 46 is a permanent ring-shaped magnet 52 (see Figs. 2, ll) whose lower surface is coplanar with the lower surface of shield body 45. Magnet 52 may be made of any one of a number of special alloys which can be highly magnetized in manufacture, and which is magnetically stable in storage and under conditions of vibration, shock, temperature, and the like.

Resting adjacent shield body 45 and magnet 52 in the same recess with the shield body is shear plate 37 made of insulating material (see Figs. 2, 5, 11, 11A) and having a central opening 54, opposed tabs 55 projecting into the central opening, and a small eccentrically located opening 56. Central opening 54 is slightly greater in diameter than the ring magnet 52, while the least diameter across tabs 55 is slightly greater than the central hole of the magnet. Tabs 55, therefore, serve as a barrier which prevents axial movement of ball ring 35 and magnet 52 until such movement becomes necessary. The area of shear of tabs 55 is such as to prevent only a desired amount of resistance to the magnets axial move ment. Small opening 56 is the same radial distance from the axis of shear plate 53 as insulator 50 (see Figs. 2, 5).

In order to hold two-piece inductor shield 36 and shear plate 37 in place within nose 17 we have provided the externally threaded, ring-like, non-conductive end plug Contained within the coil shield and wound upon 38 (see Figs. 2, 11 and 11A). The central opening of this plug is slightly greater than the outer diameter of magnet 52.

Plug 38 contains a set-in metallic contact ring 53 whose upper surface is slightly above the plugs upper face, and whose mean radius is in alignment with insulator 50 through which passes one end 49 of coil 48. Securely attached to this contact ring, by any conventional means, is a metallic terminal post 59 which passes through an accommodating opening in the end plug (see Figs. 2 and 11A).

Before inserting end plug 38, a part of wire 49 from coil 48 is stripped of insulation and made to lie fiat against the adjacent face of shear plate 37 so that when the plug is threadedly attached to nose 17, wire 49 is pressed between shear plate 37 and contact ring 58, thus effecting good electrical contact as at location B (see Figs. 2 and 12).

Plunger, arming balls and shear balls Axially accommodated within nose 1'], ball ring 35 and magnet 52 is the metallic plunger 60 having (from front to rear) a cylindrical shank 61, which is a slide lit in recess 33, a flange 62 which is a slide fit in recess 34, a body 63 which is a slide fit in ball ring 35 and in magnet 52, a neck 64 of somewhat lesser diameter, and a slender tip 65 (see Figs. 2, 11 and 11A).

Near the plungers leading end is a circumferential, fiat bottomed groove 66 having the lower inclined side 67 (see Figs. 2, 10, 11 and 11A). The angular relationship between inclined shoulder 39 and inclined side 67 is such that these two inclined surfaces approach each other in a direction away from the plungers axis, making it possible for arming balls 69 to be retained between the two surfaces, as will be described later. The depth of the groove 66 is approximately half the diameter of arming balls 69, while the space between recess 34 and plunger shank 61 is slightly greater than the arming balls diameter (see Fig. 10).

Plunger body 63 and neck 64 form at their juncture a shoulder 76, Whose width is approximately one half the diameter of the shear balls 71 which are accommodated side by side in ball ring 35 (see Figs. 2, 11 and 11A). Shear balls 71 are prevented from escaping by a washer 72 which slidably fits around plunger body 63 and which is constantly urged against balls 71 by a coil spring 73.

At its leading end, plunger 60 has an axial threaded opening 74 and a semi-cylindrical peripheral groove 75 which extends parallel to the plungers axis. The depth of the semi-cylindrical groove 75 is substantially the same as circumferential groove 66. When aligned with corresponding semi-cylindrical blind groove 46} in nose 1'7, these grooves 40 and 75 accommodate a cylindrical key '76 (see Fig. 2), whose purpose will subsequently be described.

Positions of plunger before and after arming As will become evident later, before firing, plunger 66 is capable of assuming either one of the two positions relative to nose 17. In one position the plunger is restrained against resilience of spring 73 within the nose by arming balls 69 (see Figs. 2 and 10). With the plunger in this position the arming balls are confined in the triangular space created by inclined shoulder 39 of nose 1'7, inclined side 67 of the plungers groove 66, and groove 66 itself; while shear balls 71 (see Fig. 2) are confined in another space created by washer '72, body 63 of plunger 60, recess 41 and the ball rings inclined shoulder 42. This position of plunger 66 will be referred to as the rear, safe, or unarmed position.

In the other pre-firing position, plunger 60 protrudes beyond the leading end of nose 17 under the action of spring 73 as shown in Fig. ll. The plunger moves into this position when arming balls 69 become dislodged from their Fig. 10 position, whereupon shear balls 71, by the action of spring 73, washer 72 and inclined shoulder 42, pass into the ball rings recess 43 and under the plungreferredto asthe forward or/armed position.

After the elements discussed-thus far are assembled, plunger 60 protrudes a certain distance forward of the noses leading edge (see Fig; 11). This distance is governed bythe noses tapered shoulder 39, arming'balls 69 and flange 62 of plunger 60. When so protruding the maximum available distance, arming balls 69 are confined between tapered shoulder 39- and the leading face of the plungers flange 62, while shear balls 71 are in the position earlier described.

Protective safety cap However, following assembly, it' is desirable for protection against premature firing and" other reasons not to have the leading end of plunger60 protrude from nose 1'7; and-iris likewise desirable to have the noses leading end covered. For that'purpose we provide fiat bottomed, cup-like safety cap 16 whose'wall consists of astraight portion'78parallel to the caps axis and an'inclinedportion' 79 ('se'e'Fig's. l, 2 and The closed, fiat end of cap 16 and the end face of straight wallportion 73 are perpendicular to the caps axis,-a'nd inclined portion 79 is at substantially the same angle as the lateral surface of nose 17L Secured to the closed, flat end of cap 16', by any conventional means, is an externally threaded stud 80. I

Theaxial distance fromthe inside surface of theclosed, flat end'of cap 16' to the face of wall portion 78-is slightly greater than the distance from the lower side of circumferential groove 3? to the flat" leading end of nose 1-7i This factor is responsible for the relative positioning and spacing of the cap and the nose end shown in Figs. 2 and 10, and is the means whereby an added safety feature (explained below) has been provided by our invention.

Securing plunger in unarmed position In order to place plunger 60 in the rear, safe, or unarmed position of Figs. 2 and 10 and to secure it there after manufacture, nose 17 and its assembled parts are held' with the leading end of plunger 60 toward-the ground (not shown). By using a suitable tool (not shown), the resilient force of spring 7 3 is overcome and shearballs 71 are pushedout from under shoulder 70 and back into recess 41 of ball ring 35 where they become astride body 63' of the plunger. In a similar manner, plunger 60 is pushed against resilience of spring 73 as far as it willgo into nose 17. Arming balls 69, which previous to this were resting againstthe noses inclined" shoulder 39 and the plungers shank 61, will now roll by gravity into-circumferential groove 66 in plunger 60.

The pressure which had been applied to urge the plunger into nose 17 is then released. Pressure exerted by spring 73 expanding against flange 62 tends to force plunger 60 out of the nose, but because arming. balls 69 aretrapped between the converging. inclined shoulders 39 and 67 and between the bottom of circumferential groove 66, such outward movement of the plunger is prevented until the arming balls are released.

Nose 17 and its assembled parts can now be turned upward again to the position shown in Figs. 2 and 10, and plunger 60 is rotated by any convenient means (not shown) until semi-cylindrical grooves 40 and- 75 arein alignment. Key 76 is then inserted into the recess provided by the complementary grooves 40 and 75. The plunger is thereby secured against rotation within the nose (see Figs. 2 and 3).

Safety cap 16 is then attached to plunger 60", the caps stud 80 being screwed into the plungers threaded recess 74. When fully engaged, the face of wall portion 78 abuts the corresponding side of the right-angled circumfer'ential groove 32 in nose 1'7, and this tends to pull plunger 60against arming balls 69' thereby making their escape from the previously described position impossible.

Those skilled in the art willrealize" that only one arming ball'wouldbe necessary for this purpose; but althouglrthat'is true; it isfelt' that a greater measure of certainty is provided'by the use of more than one ball.

ELECTRIC DETONATOR Having 'described the electromagnetic fuzeportion of our invention contained in nose 17,.we shall now turn our attention to the electric detonator portion whose elements arecontainediwithin metallic detonator housing 21' together with our novel safety inductance shunt.

Detonator housing and safety inductance shunt Detonator housing 21 (see- Figs. 1 and 2) isa cylindrical member having an externally threaded leading end for attachment toadapter 20, a'body- 86' of somewhat greater diameter, and a stepped downtrailing end 87 for attachment (by means not shown) to motor 22. Extending from the leading end of detonator housing 21 are an axially located threaded recess 90 and aplain, smaller diametered recess 91.

Located at the bottom of the recess 91 is the safety inductanceshunti9z which may suitably be-comprised of SOiturns ofNo; 2'8 enamelledwire-wound upon a cylindrical;- circumferentially grooved metallic coil form 93 having opposed longitudinal slots 94 and opposed blind axial holes 95' (see Figs; 2, 4 and 9). As seen from Fig. 2 one end 96 of coil 92 is soldered or otherwise bonded to thecoiliform93 in a slot 94 at the point H, to form a ground connection. The other end 97 of coil will be mentioned later.

Detonator sleeve Adjacent coil form 93 isa. cylindrical detonator sleeve 98 made. of insulating material having a threaded leading end 99' (see Fig. 2). Leadingiend' 99' is engageable with the threaded recess 90in detonator housing 21 and the remainder of detonator sleeve 98 is accommodated in the recess- 91'. Extending from the leading end 99 of sleeve 98' is an axially located recess which accommodates the detonator 101, and extending from the bottom of that recess to the lower end of sleeve 98 is a smaller diametered'recess 102 (see Fig. 2). Sleeve 98 also has a transverse groove 103 extending across its lower face (see Figs. 2', 4' and 8) and two opposed blind cavities 104 which issue from the lower face parallel to the sleeves axis and at the same radial distance from the center as the opposed blind holes 95 located in the leading end of coil form 93 (see Figs. 4, 7, and 8'). Extending through cylindrical detonator sleeve 98 from the face of leading end 99'to the bottom of groove 103 isthe passage 105 (see Figs; 2' and7).

From Fig. 4 it can be seen that coil form 93 and detonator sleeve 98 are secured against relative rotation by means of pins 106 so that groove 103 is always in alignment with theslots 94 in coil form 93. Fig. 2 shows that one wire 107 from detonator 101- passes through recess 102, along groove 103, and into a slot 94 in coil form 93 where it. is soldered orotherwise bonded to the coil form as at G to form a ground connection. The other wire 108 of detonator 101 will be discussed later.

Cup, contact sleeve and plug Above detonator sleeve 98 is a cup 109 made of insulating. material: having, a threaded lower or trailing end 110 (see Fig; 2). The leading end of cup 109 has an opening which accommodates the leading end of a metallic contact sleeve 112.

Contact sleeve 11-2 is a hollow cylindrical member having aflange 114 which has multiple perforations 115 (see Figs. 2 and 6). Flange 114 is of somewhat larger diameter than the inside diameter of cup 109, while the length of sleeve 112 is somewhat greater than the length of cup 109 for proper assembly, as shown in Fig. 2. The space inside cup 109 around contact sleeve 112 is filled with a booster powder charge 116 of some satisfact'ory composition.

As shown in Fig. 2, cup 109 is threadedly attached to detonator housing 21 at recess 90, thereby positioning contact sleeve 112 above detonator 101 so that the perforations 115 overlie the detonator.

To the lower surface of flange 114 of contact sleeve 112 two wires are soldered or otherwise bonded at points E and F, respectively (see Figs. 2 and 12). One is wire 97 from coil 92 which passes through slot 94, groove 103, and passage 105 to the flange; the other is wire 108 from detonator 161 which passes through recess 102 along groove 103 and up through passage 105 to the flange.

Contact sleeve 112 is fitted with a cylindrical, metallic contact plug 117 having a head 119 (see Fig. 2). Contact plug 117 fits sufiiciently tight in the contact sleeve 112 to establish good electrical contact. As shown in Figs. 2 and 12, a connecting Wire 120 extends from contact plug 117, to which it is attached by any conventional means as at D" to terminate post 59, to which it is similarly attached as at C. See Figs. 2 and 12.

OPERATION OF OUR INVENTION In explaining the operation of our invention we shall start with the rocket in the Fig. 1 condition, that is, as it has been unpacked after storage or shipping. Safety cap 16 is removed by unscrewing it from plunger 60 which remains in the rear, safe, or inoperative position shown in Figs. 2 and 10. With the plungerin this position, the rocket is unarmed. The rocket is then placed in a conventional bazooka gun (not shown), the gun is aimed, and the gunner (not shown) fires the rocket in any Well known manner by igniting propellant 23. As a result of the ignition of the propellant, the rocket receives what is equivalent to a sharp axial blow which causes arming balls 69 to move out of circumferential groove 66 and into the space between recess 34 and shank 61 of plunger 60. The action of spring 73 against flange 62 then causes the plunger to move forward out of nose 17 to the forward, or armed position, until flange 62 contacts arming balls 69 and presses them against tapered shoulder 39 of nose 17 (see Fig. ll).

When this happens shoulder 7% on plunger 60 is carried to a position adjacent to the upper face of ball ring 35 and substantially tangent to shear balls '71. At this point force from spring 73 constantly pushing against washer 72, causes the washer to push against shear balls 71. They, guided by inclined shoulder 42 of ball ring 35, are moved rearwardly so that they come to rest in recess 43, under shoulder 71%, at which time they also lightly contact neck 64 of plunger 60 (see Fig. 11).

Shear balls 71 are now confined in a space determined by recess 43, neck 64, and shoulder '70 from which they cannot escape. The rocket is now in the armed condition shown in Fig. 1]. In the interim that is the brief period during which the rocket becomes armed, reaction from the burning propellant 23 causes the rocket to be shot with high muzzle velocity from the gun (not shown).

Upon striking a target 121 (see Fig. 11A) plunger 60 makes first contact and is stopped. The inertia of the rest of the rocket causes it to continue moving forward. Ball ring 35 and magnet 52 are mounted in nose 17 and they naturally also should continue moving forward, but, because of the confinement of shear balls 71 by the plungers shoulder 70 they cannot continue moving forward. As a result, the inertia of the moving rocket sets up a shearing force against tabs 55 on shear plate 37.

The tabs are rather easily sheared oif and coil 48 contained in nose 17 moves rapidly past magnet 52 thereby inducing a voltage surge in the coil. Because of the rapidity of motion of the coil past magnet 52, the voltage surge is of very short duration. At any rate the electrical power generated is transmitted to contact ring 58, to terminal post 59, to connecting Wire 120, to contact plug 117 and to contact sleeve 112.

Here the power is picked up by wire 97 from the safety inductance shunt 92 and wire 103 leading to detonator 101. Because the period of the generated current is so short, coil 92 acts as an infinitely high impedance blocking the flow of the generated current through it. Therefore, substantially all the generated current is caused to flow through detonator 101. Since the circuit is complete, detonator 101 is heated to operating temperature, and consequently explodes. Flame from detonator 101 passes through perforations in flange 114 of contact sleeve 112 and ignites the larger booster charge 116. Ignition of this charge disintegrates cup 109 and ignites the main explosive charge 122 carried in body 19 of the projectile. The rest of the action is well known to those skilled in the art.

As earlier mentioned, safety inductance shunt 92 also acts to prevent accidental ignition of the explosive charge 122, as will now be explained. In the actual use of rockets equipped with our invention, it is possible that safety caps 16 will be removed from a number of rockets in advance of the time when they are actually fired. If properly handled, though, plunger 60 will remain in the rear position (see Fig. 2) and the rocket will remain in the unarmed condition until fired. However, should accidental arming occur, it is not possible by ordinary misadventure to move magnet 52 fast enough to cause detonation. For even though the voltage surge induced by the accidental motion of the magnet is applied to the detonator circuit, the frequency characteristics of this surge will be so low that its energy will be largely dissipated in the inductance shunting the detonator. By a similar action our safety inductance shunt will also prevent ignition of detonator 101 if a rocket equipped with our invention is subjected to stray electrical or magnetic fields.

SUMMARY In summarizing the action of our invention reference will be made to the Fig. 12 schematic circuit representation which those skilled in the art-know to have a certain time constant.

When the relative axial velocity of magnet 52 and coil 48 is equal to or in excess of the threshold velocity, as when the fired projectile strikes a target, the duration of the generated electromotive force (not shown) is less than the time constant of the circuit. In such a case, our safety inductance shunt 92 presents a high impedance path to the electromotive force. This causes practically all the current to flow through detonator 101, thereby activating it and causing ignition of the explosive charge carried within the projectile.

When the relative axial velocity of magnet 52 and coil 48 is less than the threshold velocity, as when the magnet is accidentally moved relative to the inductor, the duration of the generated electromotive force is greater than the time constant of the circuit. In this case, our safety inductance shunt 92 presents a much lower impedance path to the electric pulse, causing practically all the generated current to by-pass detonator 101 and to flow through the shunt, thus preventing accidental ignition of the explosive charge carried within the unfired projectile.

In cases where a projectile, fired or unfired, and regardless of whether armed or unarmed, is subjected to low frequency stray electric or magnetic fields (which might be expected to be unaffected by the shielding effect of the actual parts of the rocket assembly), our safety inductance shunt 92 will prevent premature ignition of the explosive charge. This safeguard is assured because the shunts electrical properties are such that the low electrical current likely to be generated by such stray fields is prevented, due to by-passing action of the inductance shunt, from reaching detonator 101 in any appreciable amount.

From the foregoing it will be seen that we have provided a small, lightweight, simply constructed electromagnetic fuze-electric detonator combination whose circuit has a very small time constant, and that we have provided an electromagnetic fuze-electric detonator comto accidental physical-shock or tos'ti'aye'lectric'oi'fihagnetic fields.

Our invention is extensive in its adaption and 1s not to be restricted to the specific form here shown by way of illustration.

We claim:

1. In a fuze, a casing having an axially disposed cylindrical cavity which is tapered toward its forward end, a firing mechanism including a cylindrical plunger which is mounted in an unarmed position within said cavity but is axially movable a limited distance out of said casings forward end to an armed position, and which has a circumferential recess near the plungers forward end, a shoulder defining the rearward limit of the lungers cucumferential recess and being tapered so as to converge rearwardly toward the tapered sidewall of said casings cavity, and at least one arming ball normally positioned between the tapered wall of the cavity and the inner wall of the plungers recess so as to constrain the plunger agalnst forward movement until an adequate forwardly acting force is applied against the fuze, whereuon the arming ball becomes dislodged from its position between the tapered cavity wall and the plunger recess wall and the plunger is free to move past the arming ball and out of the casing into the armed position.

2. In a fuze, a casing having an axially disposed cylindrical cavity which is tapered toward its forward end, a firing mechanism including a cylindrical plunger which is mounted in an unarmed position within said cavity but is axially movable a limited distance out of said cavitys forward end to an armed position, and which has a circumferential recess near the plungers forward end, a shoulder defining the rearward limit of the plungers circumferential recess and being tapered so as to converge rearwardly toward the tapered sidewall of said casings cavity, a flange extending laterally from said plunger and to the rear of said shoulder, a stop mounted in said casing adjacent said plunger and to the rear of said flange, an expansible spring extending between said flange and said stop constantly tending to urge the plunger to move forwardly, and at least one arming ball normally positioned between the tapered wall of the cavity and the inner wall of the plungers recess so as to constrain the plunger against forward movement until an adequate forwardly acting force is applied against the fuze, whereupon the arming ball becomes dislodged from its position between the tapered cavity wall and the plunger recess wall and the plunger is moved forwardly under the urging of said spring past the arming ball until at least a portion of the plunger exits from the easing into the armed position.

3. In the fuze of claim 1, a substantially cup-shaped safety cap adapted so that its sidewalls fit snugly against the external casing wall but its inner base surface is spaced from the casing, and a stud projecting from said caps inner base surface for threadable engagement with the leading end of said plunger, whereby tightening of the caps stud tends to draw the plunger forwardly so that its tapered shoulder pushes the arming ball forcefully against the tapered sidewall of the casings cavity and thus positively prevents further forward movement of the plunger into the armed position.

4. In the fuze of claim 1, a substantially cup-shaped safety cap adapted so that its sidewalls fit snugly against the external casing wall but that its inner base surface is spaced from the casing, a stud projecting from said caps inner base surface into threadable engagement with the leading end of said plunger for securing the plunger in a position which prevents its movement into the armed position, and means for securing said plunger against rotation relative to the casing so as to enable ready threading of said stud into said plunger.

5. In an electromagnetic fuze; a casing having an axially disposed cylindrical cavity which is tapered toward TO its-forward end; a firing mechanism including a cylindrical plungerwhich is mountedlinan unarmed position with'in:saidcavity butfis axially movable a limited dis tance out of said' cavitjys forward end to an armedposition;"the plunger having a broadened forwa'rdand'rean ward narrowed portions separated by a shoulder, a flange extendinglaterallyt fromsaid plunger; a washer encircling said plunger in slide-fitting relationship. to the rear of said flange; aball ririg' encircling said plunger and fixed in said casing against fQrWardmOi/ement behind said washer, the ring having a broadened diameter at its forward end and a lesser diameter at its rearward end; at least one shearing ball seated in said ball-rings broadened diameter when said plungers broadened forward portion is adjacent thereto but movable into said ball-rings lesser diameter when said plungers narrower rearward portion is adjacent thereto; an expansible spring extending between said flange and said washer constantly tending to urge the plunger to move forwardly and to urge the washer rearwardly to maintain contact with the shearing ball which prevents the ball from falling forwardly out of the ball-ring; a magnet encircling said plunger and fitted at its forward end against the rear end of said ball-ring; a wire coil encircling said magnet and mounted for relative axial movement with respect thereto; and a shear plate fixed in said casing and having a readily shearable tab which supports the magnet and coil against movement relative to each other until the tab is shorn; whereby impact of the fuze with its target will cause the plunger in the armed position to furnish resistance transmissible through the shearing ball, which is then held in the ball-rings lesser diameter by the plungers shoulder and narrowed portion, the ball-ring and the magnet to the shear tab which shears off as inertia carries the other fuze parts forward to generate electrical power as the coil is moved relative to the magnet.

6. In a coacting electromagnetic fuze and electric detonator, the combination of a casing having a forward nose portion and a rearward body portion, a plunger mounted within said casings nose for limited axial movement and emergence from the leading face of said nose portion; means for securing said plunger in unarmed position entirely within said casing until freed from such restraint by application to said casing of a forwardly acting force of predetermined minimum amount, a magnet encircling said plunger, a wire coil encircling said magnet and mounted for relative axial movement with respect thereto, means for securing said coil in fixed position relative to said magnet until freed from such restraint by receiving an adequate rearwardly acting force transmitted by said plunger, an electrically operable detonator mounted within said casings body portion, a safety inductance shunt, and electricity conducting means forming an electrical circuit by connections with said coil, det onator and shunt arranged so that the shunt is operable across the detonator, whereby the detonator is ignited when and only when a predetermined minimum electrical power is generated by relative movement between the coil and the magnet.

7. The combination, in an explosive projectile, of: an electric generator, said generator comprising a coil and a magnet movable relative to each other, and said generator developing electric power when the coil and the magnet are given relative movement as upon impact of the projectile, the power output of said generator being responsive to the velocity of the relative movement between the coil and the magnet; an electric detonator connected to said generator, said detonator being operable to explode the projectile upon receiving a predetermined minimum of electrical power from said generator; a shunt across said detonator, said shunt having such impedance that it acts as a low resistance to electrical power below a predetermined minimum but acts as a high resistance to electrical power above a predetermined minimum; whereby upon high velocity impact of the projectile, said generator 11 12 develops electric power which by-passes said shunt and FOREIGN PATENTS activates said detonator to explode the projectile, where- 24225 France 30 1921 as upon low velocity impact of the projectile, said gen- (Addition to No. 528,187) erator develops electric power which by-passes said detonator, thus avoiding activation thereof, and passes 5 through said shunt.

References Cited in the file of this patent UNITED STATES PATENTS 1,133,183 Reineke Mar. 23, 1915 10 

